Hi. My name is Friday—Joe Friday. I'm a calculus student. I want to tell you a little story—a story about parabolic boulevards, focal fountains, and a car speeding through the night. I like to call it … the Case of the Swiveling Spotlight.

It all started one bleak Monday evening in early November. I'd gotten home from classes, made some sandwiches, and settled down with a tall glass of something cold when the phone rang. It was my older sister Delia. Delia's a smart woman—she graduated from Law School a few years ago and now she's working for a law firm in Lac du Portage, a small town southeast of here. As soon as she started talking I could tell that she was worried.

“Joey, I've got a problem. A real problem. I've been hired to defend a local citizen on a charge of speeding. He's already had a few traffic citations, and if he's convicted this time he's sure to lose his license. Our only hope is to convince the judge that the police don't have enough evidence. But the case comes to trial in 17 days, and I need to have a written brief to present to the judge by that time. When I described the case to my secretary Perry, he told me that he thought that it might involve calculus. You're the only person I know whose calculus is up to date. Joey, you've got to help me!”